The present invention relates to optical amplifiers, and more particularly to a compact, low cost optical amplifier package having a small optical waveguide amplifier chip and an optical pump integrated therein.
The field of optical telecommunications has experienced phenomenal growth over the past several years, fueled in large part by the development and deployment of erbium-doped fiber amplifiers (xe2x80x9cEDFAsxe2x80x9d).
Prior to optical amplifiers, fiber optic communication systems required electronic repeaters to amplify signals and offset the losses associated with long distance optical transmission. These electronic devices converted the transmitted optical signal into the electrical domain, amplified and reshaped the electrical signal, and converted the electrical signal back into an optical signal, and onto the next leg of the fiber system.
Electronic detectors are incapable of discriminating between different wavelengths, therefore, multi-wavelength systems require an independent repeater for each wavelength in the system, as well as the necessary filtering components to isolate each of the wavelengths into their respective repeaters. FIG. 1a is a representative bock diagram of a 16 channel repeater system 10. The large amount of equipment needed made multi-wavelength communications systems using repeaters prohibitively expensive.
The deployment of the EDFA, however, changed the topology of fiber-optic communication networks. Because the optical amplifier was capable of amplifying multiple wavelengths independently in a single unit, a multi-wavelength system could use a single optical amplifier. The 16 channel repeater system of FIG. 1a requires a wavelength de-multiplexer 12 to break the 16 channels out onto individual fibers 14, 16 repeaters 18, and a wavelength multiplexer 16 to re-combine the 16 individual wavelengths. All of this was replaced by the single EDFA 20 shown in FIG. 1b. 
This ability to add multiple channels to a single fiber with minimal additional amplifier costs created an explosion in the bandwidth of optical fiber communication systems. Deployed systems went from single channel sub-gigabit per second operation to 128 channel, multi-gigabit per second per channel operation.
The continuing growth in the bandwidth of optical communication systems has also led to a new demand for more complex functionality in optical networks. To satisfy this demand, manufacturers are desirous of devices in increasingly smaller and more compact packages, while at the same time integrating multiple functions into a single device. In sharp contrast to the ever-shrinking size of many optical network components, the EDFA faces a hard limit because of the fixed value of the minimum bend radius of the fiber. Bend losses are proportional to the bend radius, and hence the radius must be kept large. A nominal radius for such fiber is about 3.75 cm, resulting in a coil diameter of about 7.5 cm (about 3 inches) which in turn results in an minimum package planar dimension of at least 3xc2xdxc3x973xc2xd inches. Consequently, though many components such as the isolators, 980/1550 nm multiplexers, and monitor taps and photodiodes can be integrated into the package, the footprint remains constrained by the minimum diameter of the erbium-doped fiber coil. Nominal package dimensions are now about 6xc3x976 inches.
Semiconductor optical amplifiers (SOAs) are also available, and rely on electrical (rather than optical) pump sources for amplification. However, their performance characteristics are known to be deficient in many areas, compared to EDFAs.
The demand for more compact devices with greater integrated functionality is accompanied by the need to reduce the cost of these devices. As optical system designers increase the complexity of their networks, the number of optoelectronic components required grows substantially. For the very same reasons that multi-wavelength systems with electronic repeaters were prohibitively expensive, more complex networks begin to face the same cost issues. Thus, not only is xe2x80x9creal estatexe2x80x9d within the system at a premium requiring smaller, integrated devices, but cost also plays a significant role requiring less expensive components as well.
The EDFA was the critical enabling technology that gave rise to the recent boom in optical communications known as WDM. As communications systems continue to grow and expand, system designers find themselves in need of new devices, amplifiers in particular, that are smaller and less expensive than their current counterparts. A compact, low cost optical amplifier with the ability to incorporate additional devices for added functionality is therefore required.
The shortcomings of the prior approaches are overcome, and additional advantages are provided, by the present invention which in one aspect is an optical amplifier having a housing with optical signal input and output ports; a channel waveguide chip in said housing for optically amplifying an input optical signal from the input port using an optical pump signal applied thereto; and an optical pump source in the housing for generating the optical pump signal.
The amplifier may also include input coupling optics for transmitting the input optical signal into the channel waveguide chip from the input port; and output coupling optics for carrying an output optical signal from the channel waveguide chip to the output port.
In one embodiment, the channel waveguide chip includes a linear core having an input end for receiving an input optical signal, and an output end for producing an output optical signal; and a surface through which the optical pump signal is received. The surface of the channel waveguide chip may be arranged at an approximately 45 degree angle with the linear core thereof. The optical pump source transmits the optical pump signal at approximately a 90 degree angle with the core. The chip may also include a reflective coating applied over the surface to reflect the optical pump signal into the linear core. A prism may be applied over the surface for directing the input optical signal colinearly into the core.
The optical pump source may be a laser diode which generates the optical pump signal internal to the housing, wherein the only optical ports of the amplifier are the optical signal input and output ports.
Based on the types of components used, the present invention attains a package dimension of less than about 3 inches in at least one planar dimension.
The amplifier disclosed herein provides, in a compact, cost-effective package, a channel waveguide amplifier chip, appropriate optics to couple the signal into and out of the waveguide, a pump laser diode, and appropriate optics to focus the light from the pump laser diode into the waveguide. In addition, the amplifier may also be constructed to integrate additional optical components for added functionality. This invention therefore provides significant optical amplification in a low-cost, compact package that can minimize the space required within a communications system to provide signal amplification, and be integrated with additional components, such as splitters, wavelength multiplexers or demultiplexers, or optical add/drop multiplexers.